1. Technical Field
The present invention relates to a field-effect transistor, a semiconductor wafer, a method for producing a field-effect transistor, and a method for producing a semiconductor wafer.
2. Related Art
A metal-insulator-semiconductor field-effect transistor (MISFET), which uses a compound semiconductor for its channel layer, is expected to serve as a switching device suitable for high-frequency and higher-power operation. The MISFET, however, encounters a problem where the carrier mobility may fall when an energy level is formed at the interface between the semiconductor and the insulator. Non-Patent Document 1 discloses that the energy level formed at the interface between the semiconductor and the insulator (herein referred to as “the interface state”) can be effectively reduced by treating the surface of the compound semiconductor with sulfide.    Non-Patent Document 1: S. Arabasz, et al., Vac. Vol. 80 (2006), page 888
It is, however, desired to further reduce the interface state. It is also desired to improve the performance of the field-effect transistor by employing a technique of reducing the influence of the interface state even if the interface state exists. An object of the present invention is to provide a field-effect transistor having a high channel mobility while keeping the influence of the interface state low.